Hydroxyapatite	x¹	gm
Dispersant	1.0	wt % of x
Acrylamide	4	gm
Surfactant	0.1	gm
Methylenebisacrylamide	0.5	gm
Ammonium persulphate	0.1	gm
N,N,N N′	0.1	gm
tetramethylethylenediamine

¹x = 35, 40, 45 or 50.

The slurry was deagglomerated by ball-milling for 24 hours, and subsequently de-aired under vacuum until no further release of air bubbles occurred from the slurry. Catalyst (ammonium persulphate) and initiator (N,N,N,N′ tetramethylethylenediamine) were added to the slurry to polymerize the monomers. Pieces of polyurethane foam, cut into a desired shape and size, were completely immersed in the slurry under vacuum to allow the hydroxyapatite powder particles to migrate into the pores of the foam. The amount of the catalyst and initiator were controlled to allow a sufficient time for the slurry to impregnate the polyurethane foam before gelation.

The pieces of foam were taken out of the slurry and placed in a nitrogen chamber to avoid oxygen contamination which may inhibit the polymerization process. The polymerized samples were dried in air for 24 hours, then the samples were heated at a rate of 1° C./min to 600° C. The samples were heated at this temperature for 1 hour to burn out the polyurethane foam, and then sintered at a rate of 3° C./min to 1350° C. for a dwell time of 2 hours. The process of polymer burn out was incorporated with sintering to avoid handling the ceramic structure.

Thermogravimetric Analysis: Thermogravimetric analysis (TGA) is used to measure thermal stability and composition of a material. TGA measures weight changes in a material as a function of temperature (or time) under a controlled atmosphere. TGA was used to study the pyrolysis process of the polyurethane foam, and was used to determine the temperature for incinerating the polyurethane foam. TGA was performed in a vertical tube furnace, using Netzsch STA 409C, with a heating rate of 1° C./min up to 600° C. under nitrogen flow.

Porosity and Density Measurements: A liquid displacement method was used to measure the porosity and density of the hydroxyapatite scaffolds. Density measurements provided information about pore size and distribution, permeability, and presence of structural faults in the sintered ceramic structures (see, e.g., Sepulveda, P.,Am. Ceram. Soc. Bull.76: 61-65 (1997)). A scaffold of weight W was immersed in a graduated cylinder containing a known volume (V₁) of water. The cylinder was placed in vacuum to force the water into the pores of the scaffold until no air bubbles emerged from the scaffold. The total volume of the water and scaffold was then recorded as V₂. The volume difference (V₂-V₁) was the volume of the skeleton of the scaffold. The scaffold was removed from the water and the residual water volume was measured as V₃. The total volume of the scaffold, V, was then
V=(V₂−V₁)+(V₁−V₃)=V₂−V₃ (1)

The density of the scaffold, ρ, was evaluated as,

\begin{matrix} ρ = \frac{W}{(V_{1} - V_{3})} & (2) \end{matrix}

The porosity of the open pores in the scaffold, ε, was evaluated as,

\begin{matrix} ɛ = \frac{(V_{1} - V_{3})}{(V_{2} - V_{3})} & (3) \end{matrix}

X-Ray Diffraction Analysis: X-ray diffraction (XRD) was used to characterize the crystallinity, chemical composition, and structure of materials. XRD experiments were performed on both hydroxyapatite powder and the sintered scaffolds after being crushed to powder with a Phillips X'Pert, using CuK_α radiation at 20 mA, 40 kV. Scans were performed between 20 values of 10° and 70° at a rate of 0.4°/min.

Infrared Spectroscopy: Infrared Spectroscopy was used to characterize hydroxyapatite powder before and after sintering. A dried sample of 2 mg was carefully mixed with 300 mg dry KBr and pressed into a pellet using a macro KBr die kit. The solid pellet was placed in a magnetic holder. The system was purged with dry air for 1 hour to remove water vapor from the sample compartment. Polarized Fourier Transformed Infrared (FTIR) spectra of 2000 scans at 8 cm⁻¹were obtained using a Nicolet 5DX spectrometer with a DTGS detector and a solid transmission sample compartment. Spectrum analyses were performed using standard Nicolet and Microcal Origin software. FTIR spectra were taken on both hydroxyapatite powder (used to make the sintered scaffolds) and sintered hydroxyapatite powders prepared from the sintered scaffolds.

Mechanical Testing: One of the major problems for mechanical characterization of porous ceramic scaffolds is the difficulty in machining and gripping the specimen; hence the conventional methods of mechanical characterization such as tensile, biaxial and impact testing are usually inapplicable to porous materials (see, Currey, J. D.,Clin. Orthop. Rel. Res.73: 210-231 (1970)). Instead, the compression test has been widely accepted and used successfully for characterization of cance/lous bone and porous hydroxyapatite (Hodgskinson, R., and J. D. Currey, Proceedings of the Institute of Mechanical Engineers, Part H:J. Eng. Med.204: 115-121 (1986); Hing, K. A., et al.,J. Mater. Sci.10: 135-145 (1999)).

An Instron 4505 mechanical tester with a 10 KN load cell was used for the compression mechanical test using the guidelines set in ASTM D5024-95a. The cross head speed was set at 0.4 mm/min, and the load was applied until the scaffold was cracked. The elastic modulus was calculated as the slope of the initial linear portion of the stress-strain curve. The yield strength was determined from the cross point of the two tangents on the stress-strain curve around the yield point.

Scanning Electron Microscopy (SEM): A JEOL 5200 scanning electron microscope was used for morphological characterization of scaffolds. The samples were coated with gold/palladium under an argon atmosphere. Energy dispersive spectroscopy (EDS) (Tracor Nothem 5200) was used to provide qualitative information on the elemental composition of scaffolds.

Results: The hydroxyapatite scaffolds produced by the methods described in this Example had a three-dimensional polymeric network of pore walls composed of a substantially homogeneous polymer matrix (that did not exhibit significant hydroxyapatite particle sedimentation). Scaffolds with different geometries were formed by cutting the polyurethane foam into the required shape. Different pore sizes and geometries were achieved by using polyurethane foams having different, desired, porous structures.

Four different concentrations of hydroxyapatite slurries, 35%, 40%, 45% and 50%, were selected to evaluate the effect of hydroxyapatite concentration on the physical and mechanical properties of scaffolds. In general, increasing the concentration of hydroxyapatite increases the density, and improves the mechanical properties, of the sintered product, and reduces excessive sample shrinkage (Lange, F. F., and M. Metcalf,J. Amer. Ceram. Soc.68: 225-231 (1985); Omatete, O. O., et al.,Am. Ceram. Soc. Bull.70: 1641-1649 (1991). High concentrations of hydroxyapatite produce a high viscosity slurry, causing difficulty in proper mixing and slurry impregnation in a polymer sponge. Therefore, 50% concentration of hydroxyapatite was selected as the highest concentration used in this experiment. The amounts of polymerizable monomers and hydroxyapatite (Table 1) were selected to obtain a uniform and workable slurry (Young, A. C., et al.,J. Am. Ceram. Soc.74: 612-618 (1991); Omatete, O. O., et al.,Am. Ceram. Soc. Bull.70: 1641-1649 (1991).

Colloidal studies on hydroxyapatite powders have shown that polyacrylate is a suitable dispersant for aqueous hydroxyapatite slurries (see, e.g., Rodriquez-Lorenzo, L. M., et al.,Biomaterials22: 1847-1852 (2001)). Darvan C, a polymethacrylate, was chosen as the dispersing agent in this study. The amount of the dispersant added affects the sintering behavior and hence mechanical properties of the scaffolds. All the slurries prepared in this study contained 1 wt % of Darvan C. Surfonal® in the slurry acts as an antifoaming agent that reduced the tendency of the formation of bridging between cell walls (see, U.S. Pat. No. 3,907,579, 1975.). Air bubbles entrapped in the slurry can lead to closed pores in the ceramic structure after drying, which decreases the density and thus mechanical strength of the ceramics (Omatete, O. O., et al.,Am. Ceram. Soc. Bull.70: 1641-1649 (1991), therefore the slurry was deaired after ball milling.

The initiator and catalyst were added to the slurry to polymerize the monomers. The polyurethane foam of desired shape was immersed in the slurry under vacuum to allow complete impregnation of the slurry into the foam. The polyurethane foam impregnated with hydroxyapatite slurry was then taken out of the slurry and placed in a nitrogen atmosphere to promote polymerization of the acrylamide monomers.

In the polymer sponge method the slurry can settle down at the bottom of the polyurethane foam during the drying process which results in a non-homogeneous porous structure after sintering. One of the advantages of the method described in this Example is rapid polymerization of slurry within the polyurethane foam resulting in a homogeneous, thick walled microstructure. Rapid drying of gelled materials formed after polymerization can cause non-uniform shrinkage leading to material cracking or warpage. Consequently, in the experiments reported in this Example the polymer foam, impregnated with hydroxyapatite slurry, was dried slowly in air for 24 hours.

The polyurethane foam should be incinerated before sintering the ceramic structure to avoid cracks in the microstructure of the ceramic structure. Thermogravimetric analysis (TGA) is one method to determine the temperature at which the complete burnout of the polyurethane foam occurred. TGA analysis showed that the polyurethane foam was completely burned out at 550° C. Thus, to allow ample time for the complete incineration of the polyurethane foam within the hydroxyapatite scaffolds before the sintering started, the heating rate was set to 1° C./min up to 600° C. with a dwell time of 1 hour.

At temperature above 1200° C., hydroxyapatite can become unstable and may lose OH groups to form decomposed products such as tetracalcium phosphate, and calcium oxide (Tampieri, A., et al.,J. Mater. Sc. Mater. Med.8: 29-37 (1997)). Although pure hydroxyapatite is known to be biocompatible, variations in the precise nature of the forms of calcium phosphate can have a strong effect on the cellular response of cells growing within the scaffold, and thus reduce the biocompatibility of the material (Best, S., et al.,J. Mater. Sci. Mater. Med.8: 97-103 (1997); Eggli, P. S., et al.,Clin. Orthop. Rel. Res.232: 127-138, (1988)).

Furthermore, changes in the degree of crystallinity and purity may also lead to variations in the level of scaffold solubility, which would likely affect the rate of scaffold degradation within a living body. Several authors reported the decomposition of hydroxyapatite powder at temperatures above 1150° C. (Tampieri, A., et al.,J. Mater. Sc. Mater. Med.8: 29-37 (1997)). Thus preserving the composition and crystalline structure of hydroxyapatite during sintering helps ensure that the hydroxyapatite structures are useful for biological applications. A comparison of the XRD patterns of the hydroxyapatite powder used to make the porous hydroxyapatite scaffolds and of the porous hydroxyapatite scaffolds sintered at 1250° C. and 1350° C. showed that the XRD peaks of all three diffraction patterns agreed well with those of standard hydroxyapatite in the Powder Diffraction File (PDF Card No. 9-432). No discernible difference among the three patterns was observed, and no additional phase was identified. This result indicates that the sintering process did not change the composition of the hydroxyapatite. This high thermal stability of the hydroxyapatite scaffolds allows for preparation of a fully densified, porous, hydroxyapatite structure at high sintering temperatures.

The energy dispersive spectrum (EDS) of a porous hydroxyapatite scaffold, prepared using a 45 wt % hydroxyapatite slurry, showed that the stoichiometric ratio of hydroxyapatite was retained after sintering, as suggested by XRD and IR spectroscopy. The scaffolds were made almost entirely of Ca and P with a Ca/P ratio of 1.7 as calculated from the areas enveloped by the spectrum curves of calcium and phosphorous. This result shows that little, if any, other calcium phosphate derivatives, which may affect the solubility, mechanical strength, and biological properties of the scaffolds, existed in the porous hydroxyapatite scaffolds.

The chemical composition of the porous hydroxyapatite scaffolds was further investigated using FTIR. Hydroxyapatite powder used to make the scaffolds, and the porous hydroxyapatite scaffolds were subjected to FTIR. Table 2 shows the infrared band positions and their assignments.

	TABLE 2


		Observed vibrational
	Assignments	frequencies (cm⁻¹)

	Structural OH	3570
	H₂O absorbed	3470
	Soluble CO₂(ν₃)	2300
	H₂O absorbed (ν₂)	1650
	CO₃⁻group (ν₃)	1460
	CO₃⁻group (ν₃)	1420
	PO₄bend ν₃	1030
	PO₄stretch ν₁	985
	CO₃⁻group	881
	Structural OH	630
	PO₄bend ν₄	570

Two bands at 631 and 3570 cm⁻¹correspond to the vibration of hydroxyl ions. The bands at 1030 and 570 cm⁻¹are the characteristic bands of phosphate bending vibration, while the band at 981 cm⁻¹is attributed to phosphate stretching vibration. The bands at 881, 1420 and 1460 cm⁻¹are indicative of the carbonate ion substitution. The bands at 1650 and 3470 cm⁻¹correspond to H₂O absorption. There was no discernible spectrum difference between the hydroxyapatite powder and hydroxyapatite scaffold, which further confirms that no chemical decomposition occurred during the hydroxyapatite sintering process.

The porous hydroxyapatite scaffolds should reproduce both the composition and pore morphology of bone to promote the growth of bone cells and blood vessels therein. SEM analysis showed the interconnected, macroporous structures of the scaffolds prepared with slurries of different hydroxyapatite concentrations. All samples exhibited a three dimensional interpenetrating network of structural members and pores. The scaffolds had an average pore size of 400 μm. It is believed that rapid vascularization is required to sustain the mechanical strength of a porous hydroxyapatite scaffold as it gradually degrades within a living body during bone remodeling. An interconnected open pore structure also allows biomolecules and degraded substances to freely flow into and out of the scaffold. A high degree of pore interconnectedness may also promote growth of cells and blood vessels throughout the scaffold.

Table 3 shows the density and porosity of hydroxyapatite scaffolds prepared from slurries of different hydroxyapatite concentrations.

TABLE 3


Hydroxyapatite Wt. %	Density (gm/cm³)	Porosity

35	0.397	71.40%
40	0.460	70.05%
45	0.499	76.90%
50	0.783	71.00%

The data set forth in Table 3 show that for scaffolds having the same porosity the density increases with increasing hydroxyapatite concentration. As the concentration of hydroxyapatite was increased, the pores became more interconnected with dense and thick pore walls. Thicker pore walls are advantageous because they confer mechanical strength on the scaffolds. Additionally, high porosity provides a high surface area/volume ratio, and thus favors cell adhesion to the scaffold and promotes bone tissue regeneration.

FIGS. 4 and 5 show the elastic modulus and compressive yield strength of the porous hydroxyapatite scaffolds prepared from slurries having different hydroxyapatite concentrations. The compression tests showed that all the samples failed in a manner similar to that for an elastic-brittle foam, exhibiting a linear elastic region followed by a collapse plateau presumably dominated by brittle fracture of the struts. Both the yield strength and elastic modulus of the scaffolds increased rapidly with the increase in hydroxyapatite concentration as a consequence of an increase in pore wall thickness and density of the scaffold. For the increase of hydroxyapatite concentration from 35% to 50%, the yield strength increased from 0.55 MPa to 5 MPa. The elastic modulus ranged from 4 GPa to 7 GPa, which is roughly comparable to those of cortical bone (˜4 GPa-17 GPa) (Currey, J. D.,Clin. Orthop. Rel. Res.73: 210-231 (1970)).

It has been reported that scaffolds fabricated by the gel casting technique have elastic modulus and compressive strengths in the range of 3.6 to 21.0 GPa and 1.6 to 4.7 MPa respectively, with both increasing as porosity decreased (Sepulveda, P., et al.,J. Biomed. Mater. Res.50: 27-34 (2000); Sepulveda, P., et al., “Properties of Highly Porous Hydroxyapatite Obtained by the Gelcasting of Foams,”J. Am. Ceram. Soc.83: 3021-3024 (2000)). It has been previously reported that hydroxyapatite scaffolds prepared by the polymer sponge method typically possessed a compressive strength of 1.2 MPa and compressive modulus of 8 MPa (Zhang, Y., and M. Zhang,J. Biomed. Mat. Res.61: 1-8 (2002)). Thus, the present invention provides porous hydroxyapatite structures that have improved mechanical properties compared to porous hydroxyapatite structures prepared using the polymer sponge method. These improved mechanical properties are likely attributable to thicker pore walls and a denser microstructure of the hydroxyapatite scaffolds.

EXAMPLE 2

This Example describes a method for measuring the compressive strength of porous ceramic structures.

A straight elastic bar of uniform cross section, A, is measured in tension by applying loads at the ends that are distributed evenly over the gage of the specimen. The stress, σ, is calculated using the force applied, F, as

\begin{matrix} σ = \frac{F}{A} & (1) \end{matrix}

Strain, ε, the normalized deformation is given by

\begin{matrix} ɛ = \frac{l_{f} - l_{o}}{l_{0}} & (2) \end{matrix}

where, l_fis the final length after testing and l_ois the initial length of the material.

The elastic modulus, E, of the material is the intrinsic property that is calculated from the slope of the linear portion of the stress strain curve, and is given by

\begin{matrix} E = \frac{σ}{ɛ} & (3) \end{matrix}

An Instron 4505 mechanical tester with 10 kN load cells is used for the compression mechanical test. The specimens to be tested are made cylindrical in shape with a length to diameter ratio of 2:1, which is designed to minimize the end effect imposed by compressive loading. The crosshead speed is set at 0.4 mm/min, and the load is applied until the specimen cracks. Yield stress and elastic modulus are calculated using Eq.1-3. Five samples of each type are tested for mechanical properties, and the results are averaged.

EXAMPLE 3

This Example describes a method for measuring the average diameter of pores in a porous ceramic structure.

A portion of a porous ceramic structure is coated with gold/palladium under an argon atmosphere. A JEOL 5200 scanning electron microscope is used to produce an image of the coated portion of the porous ceramic structure. The diameter of each pore within a square area of the image is measured. All of the diameter values are added together and divided by the number of pores that were measured. The resulting value is the average pore diameter.

EXAMPLE 4

This Example describes the preparation, and some physical properties, of porous β-tricalcium phosphate scaffolds, including hydroxyapatite nanofibers, prepared using the methods of the present invention.

Materials: β-TCP (β-Ca₃(PO₄)₂) powder was used as provided by the supplier. Darvan C (Vanderbilt Company Inc.), a 25% aqueous solution of ammonium polymethacrylate, was used as a dispersant. Monofunctional acrylamide C₂H₃CONH₂and difunctional methylenebisacrylamide(C₂H₃CONH)₂CH₂were used in the gel-casting process as the polymerizable monomers, and ammonium persulphate (NH₄)₂S₂O₈and N,N,N,N′ tetramethylethylenediamine(TEMED) as the initiator and catalyst, respectively. All of the foregoing chemicals were purchased from Sigma-Aldrich Corporation. A silicone based defoamer, Surfonal® DF 58 (Air Products and Chemicals), was used as a surfactant. All the slurries were aqueous. De-ionized (DI) water was used in all the experiments. Hydroxyapatite nanofibers were prepared with calcium nitrate tetrahydrate (Ca(NO₃)₂.4H₂O) and ammonium hydrogen phosphate ((NH₄)₂PO₄), obtained from Sigma-Aldrich Corporation. Polypropylene glycol (H[OCH(CH₃)CH₂]_nOH), used to disperse hydroxyapatite nanofibers, was obtained from Alfa Aesar Corporation.

Synthesis of HA nanofibers: hydroxyapatite nanofibers were prepared using the following chemical reaction:
10Ca(NO₃)₂+6(NH₄)₂HPO₄+8N₄OH→Ca₁₀(PO₄)₆(OH)₂+6H₂O+20NH₄NO₃
19.75 g of (NH₄)₂PO₄were added to DI water to make a 400 ml solution of diammonium hydrogen phosphate. 300 ml calcium nitrate solution were prepared by dissolving 57.5 g of Ca(NO₃)₂.4H₂O in DI water. The pH of the solution was adjusted to 10.4 by addition of NH₄OH. White precipitates of hydroxyapatite were formed by adding the diammonium hydrogen phosphate solution into the calcium nitrate solution at a rate of 1.5 ml/min under constant stirring. The white precipitates were aged for 100 hours to form hydroxyapatite nanofibers. The nanofibers were washed with DI water until the pH value decreased to 7. The water surrounding the hydroxyapatite nanofibers was then replaced with 1-butanol to prevent the hydroxyapatite nanofibers from aggregation during the drying process. The precipitates were dried at 80° C. and calcined at 400° C. to remove the rudimental organic compound.

Nanocomposite scaffolds: hydroxyapatite nanofibers were mixed with β-TCP powder, along with monomers (acrylamide, methylenebisacrylamde), dispersant (Darvan C) and surfactant (Surfonal®), to make ceramic slurries with 75 wt % solid loading. The amount of hydroxyapatite nanofibers ranged from 0, 1, 2, 3, 4 and 5 wt %. The slurries were deagglomerated by ball milling for 24 hours and subsequently de-aired under a vacuum environment until there was no further release of air bubbles from the slurries. Catalyst (ammonium persulphate) and initiator (N,N,N,N tetramethylethylenediamine) were added to the slurries to polymerize the monomers.

Polyurethane foam cut into desired shapes and sizes was immersed into the slurries under vacuum to force the ceramic slurries into the pores of the foam. The samples were placed in a nitrogen chamber during polymerization to avoid oxygen contamination, which may inhibit the polymerization process. The polymerized samples were dried in air for 24 hours and heated at a rate of 1° C./min to 600° C. The samples remained at this temperature for 1 hour to burn out the polyurethane foams, and then were sintered by increasing the temperature at a rate of 3° C./min to the sintering temperature for a dwell time of 1 hour. The sintering temperature, which depends on the hydroxyapatite nanofiber content in the scaffold, was evaluated with a dilatometer.

X-Ray Diffraction Analysis: X-ray diffraction (XRD) was used to characterize the crystallinity, chemical composition, and structure of the materials. XRD experiments were performed on hydroxyapatite nanofibers and biphasic calcium phosphate ceramics before and after sintering, with a Phillips X'Pert using CuK_α radiation at 20 mA, 40 kV. Scans were performed with 20 values from 20° to 40° at a rate of 0.2°/min.

Transmission Electron Microscopy (TEM): The morphology of hydroxyapatite nanofibers was observed with a transmission electron microscope (CM 100 TEM) at an accelerating voltage of 100 kV. Samples were prepared by drying the solution of hydroxyapatite nanofibers on a copper grid, fitted with a carbon support film, under vacuum. The solution was prepared by dispersing 0.05 gm of hydroxyapatite nanofibers in 0.5 vol % polypropylene glycol under sonication (550 Sonic Dismembrator, Fisher Scientific, Pittsburgh, Pa.).

Determination of Sintering Temperature: The sintering temperature of biphasic calcium phosphate was determined with a Netzsch Dilatometer. Samples were heated in Netzsch tube furnace from 20° C. to 1400° C. at a rate of 3° C./min.

Scanning electronic microscopv (SEM): Morphology of porous composites was studied with a JEOL 5200 scanning electron microscope. The samples were pre-coated with gold/palladium under an argon atmosphere.

Mechanical Testing: The specimens of porous scaffolds were cylindrical in shape (2 mm height×1 mm diameter) with a length to diameter ratio of 2:1. An Instron 4505 mechanical tester with 10 KN load cells was used for the compression mechanical tests. The crosshead speed was set at 0.4 mm/min, and the load was applied until the scaffold was crushed completely. The elastic modulus was calculated as the slope of the initial linear portion of the stress-strain curve. The compressive strength was defined as the maximum compressive strength obtained during testing before densification. The toughness was calculated from the area under the stress displacement curve from zero to the point where the final densification starts. The mechanical properties of five samples of each type were tested.

Results: TEM of a sample of hydroxyapatite nanofibers synthesized as described in this Example revealed that the nanofibers had a length of about 100 nm and a diameter of about 20 nm. The hydroxyapatite nanofibers, synthesized as described in this Example, were aged for 100 hours, yielding a well-crystallized structure. The aging process ensured that the reagents were fully reacted and precipitated. The prolonged aging time reduced crystal strains in the matrix and recrystallized non-homogeneous grains to generate more homogeneous grains. Comparison of the XRD pattern of the hydroxyapatite nanofibers with the diffraction pattern of standard crystalline hydroxyapatite showed that the peak locations for the hydroxyapatite nanofibers agreed well with those of standard crystalline hydroxyapatite.

The sintering temperature, at which the samples attained their minimum change in length, was 1274° C. for pure β-TCP, and was 1144° C. for the sample with 5 wt % of hydroxyapatite nanofibers incorporated. The addition of nanofibers reduced the sintering temperature of the ceramic matrix, a phenomenon attributed to their high surface reactivity. A lower sintering temperature is favored because it can reduce the cost of material processing and prevent the second phase decomposition which often occurs at high temperature and deteriorates the biological and mechanical properties of biomaterials.

The porosity of the sintered scaffolds, as measured with the Archimedes method in distilled water, was ˜73%±0.4. SEM analysis revealed that the scaffolds had an interconnected macroporous structure with a pore size in the range of 300-400 μm. The macroporous structure promotes cell growth and vascularization.

Overall, the compressive strength and compressive modulus of the scaffolds increased with increasing concentration of the hydroxyapatite fibers. The scaffold containing 5 wt % hydroxyapatite nanofibers attained a compressive strength of 9.8±0.3 MPa, which is comparable to the high end of compressive strength of cancellous bone (2-10 MPa).

Fracture toughness, the resistance of a material to crack propagation, is an important parameter to assess the susceptibility of a scaffold to failure. The fracture toughness of the porous scaffolds was evaluated by the area under the stress displacement curve from zero to the point of the maximum stress. The fracture toughness is seen to increase from 1.00±0.04 to 1.72±0.02 Mpa/mm as the concentration of HA fibers increased from 0 wt % to 5 wt %.

While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.